Small motor vehicles including motorcycles, snowmobiles, all-terrain vehicles (ATVs), and personal watercraft generally incorporate hand-operated accelerator mechanisms for modulating the power output from the engine, or in the case of electric vehicles, from the motor. Small motor vehicles are often used in competitions where the performance of the rider and the vehicle, and interactions between rider and vehicle are extremely important. To ride small motor vehicles effectively, riders, especially competitive riders, must be able move comfortably through a wide range of body postures, maintain a grip on the vehicle under extreme accelerations and, at the same time, precisely and uninhibitedly modulate the vehicle controls. These requirements and the need to address them all simultaneously, pose difficult challenges for development of new accelerator designs.
Several standard accelerator designs are employed with varying degrees of popularity among the various types of small motor vehicles. Each standard design suffers from one or more shortcomings relating to the three areas of body posture; grip maintenance; and precise, uninhibited control modulation.
Motorcycles in particular, commonly employ a rotatable hand grip coupled by a cable or pair of cables to an engine's throttle valve. The rider rotates her wrist while gripping the handlebars to control the vehicle's acceleration. These rotatable grip accelerators cause problems in all three areas identified above. When a rider demands maximum acceleration, to rotate the grip fully, she must either: bend her wrist upward sharply and lower her elbow, or temporarily let go of the handlebar in order to overgrip as discussed in the article: Pete Peterson. “Overgrip/Regrip With Gary Semics” Dirt Rider November 2009. Bending the wrist sharply is difficult because the aggressive acceleration subjects the wrist and forearm to substantial tension. Lowering the elbow also restricts and contorts the body position of the rider, adversely impacting rider performance and riding experience.
Thumb-lever accelerator mechanisms are commonly used on ATVs, snowmobiles and personal watercraft. Thumb-lever accelerators are lacking in that they prevent the rider from fully engaging her thumb with the handlebar grip. Full engagement of the thumb with the handlebar is necessary to grip the handlebar tightly. Consequently, thumb lever controls substantially reduce the rider's ability to hang onto the vehicle when encountering severe bumps.
Index-finger lever accelerators, including those discussed in U.S. Pat. Nos. 6,393,933, 5,775,167 have been developed which attempt to address the problems associated with thumb and twist-grip accelerators, but these known technologies introduce different drawbacks. Known index finger accelerators have arrangements similar to those of brake or clutch levers, which include a lever that pivots on an axis that is perpendicular to the handlebar axis, thereby letting the rider pull an end portion of the lever towards the handlebar with one or more fingers. These accelerator arrangements require an unnatural movement of the index finger. Further, the design similarities between these devices and brake lever mechanisms make it difficult to combine both brake and accelerator mechanisms on one end of a handlebar for operation by the same hand. When combining brake and accelerator mechanisms mechanical interference is difficult to avoid, and the two levers are easily confused by the rider because their positions and actuation motions are similar. These arrangements work well for clutch and brake levers but poorly for accelerators.
To understand more fully why the known finger-lever accelerators give rise to an unnatural finger motion, one must make a few observations about the human index finger. The index finger comprises three joints that connect the phalanges of the hand; moving from the base of the finger towards the finger tip, one finds: the metacarpophalangeal joint, the proximal interphalangeal joint, and the distal interphalangeal joint. The proximal and distal interphalangeal joints are hinge joints and therefore permit substantial motion only in one plane, namely flexion and extension. The metacarpophalangeal joint permits some motion in all three planes, but with greatest mobility in flexion and extension. Because all three joints have much greater mobility in flexion and extension than any other motion, the finger tip is primarily mobile in a single plane, relative to the rest of the hand. Known finger-lever accelerators move in manners that have the operating fingertip deviate significantly from this plane of maximum mobility, thereby causing discomfort, fatigue, or inhibited control motion.
Electronics have been used as well in accelerators. US patent application publication 2006/0219455A1 and U.S. Pat. No. 6,371,890 discuss arrangements using torque sensors in a rotatable grip for modulating fuel and air input to the engine in response to torque applied to the hand-grip. While this theoretically avoids the body posture restrictions and grip-releases of conventional twist-grips, these designs give rise to significant positive feedback on the control from the hand reacting to acceleration of the vehicle. This positive feedback can greatly reduce the precision with which the accelerator can be controlled.
U.S. Pat. Nos. 6,551,153 and 7,581,464 discuss arrangements using position sensors attached to finger-levers or linearly-constrained thumb controls. These designs have grip strength and range-of-motion drawbacks similar to the drawbacks of their widely used mechanical counterparts.
Thus there remains a considerable need for a small vehicle accelerator that provides precise, uninhibited access to the full throttle range with a minimal impact on rider's body position and grip strength, with minimum feedback from acceleration of the vehicle and with an acceptable geometry to avoid mechanical interference with a brake lever.